在.net web應用程序開發中, 我們希望用戶在做一個重要的操作時, 能夠詢問或警告用戶. 或者希望我們有這么一個簡單實用的控件, 能在用戶確定后引發一個服務端的事件.
這個控件的原理很簡單,主要是實現ipostbackeventhandler接口和調用page.getpostbackeventreference(this, eventargument), 實現對客戶端__dopostback方法的調用, 引發服務端的事件
而以下這段關鍵代碼是實現功能的核心:
if(alertstring != "") //僅在用戶確認后調用客戶端的__dostpostback, 引發服務端事件
{
action = "javascript:if(window.confirm(/'" + alertstring + "')==true){";
action += page.getpostbackeventreference(this, "click");
action += ";}";
}
全部代碼:
using system;
using system.web.ui;
using system.web.ui.webcontrols;
using system.componentmodel;
namespace booksir.webcontrols
{
/// <summary>
/// alertbutton 的摘要說明。
/// </summary>
[
defaultproperty("text"),
toolboxdata("<{0}:alertbutton runat=server></{0}:alertbutton>"),
system.componentmodel.defaultevent("click"),
]
public class alertbutton : system.web.ui.webcontrols.webcontrol, ipostbackeventhandler
{
private viewstatebag statebag;
public alertbutton()
{
statebag = new viewstatebag(this.viewstate);
}
public event eventhandler click; //事件句柄
public enum appearanceenum
{
button,
imagebutton,
}
/// <summary>
/// 按鈕的外觀模式
/// </summary>
[
bindable(false),
category("appearance"),
defaultvalue(appearanceenum.button),
description("按鈕的外觀模式"),
]
public appearanceenum appearance
{
get
{
object obj;
obj = viewstate["appearance"];
if(obj == null)
{
appearance = appearanceenum.button;
return appearanceenum.button;
}
return (appearanceenum)obj;
}
set
{
viewstate["appearance"] = value;
}
}
/// <summary>
/// 在defaultvalue為非常量值的情況下,可以用reset...來重置屬性的默認值
/// </summary>
void resetappearance()
{
appearance = appearanceenum.button;
}
/// <summary>
/// 該方法的存在使系統在屬性為默認值不提交屬性賦值代碼
/// </summary>
/// <returns></returns>
bool shouldserializeappearance()
{
return appearance != appearanceenum.button;
}
[
bindable(true),
category("appearance"),
defaultvalue("")
]
public string text
{
get
{
return statebag.getstring("text", this.id);
}
set
{
viewstate["text"] = value;
}
}
/// <summary>
/// 在執行動作前的提示
/// </summary>
[
bindable(true),
category("appearance"),
defaultvalue(""),
description("在執行動作前的提示"),
]
public string alertstring
{
get
{
return statebag.getstring("alertstring", "是否開始執行?");
}
set
{
viewstate["alertstring"] = value;
}
}
/// <summary>
/// 按鈕可用時的image
/// </summary>
[
description("按鈕可用時的image"),
category("appearance"),
editor(typeof(system.web.ui.design.urleditor), typeof(system.drawing.design.uitypeeditor)),
]
public string enabledimage
{
get
{
return statebag.getstring("enabledimage", "");
}
set
{
viewstate["enabledimage"] = value;
}
}
/// <summary>
/// 按鈕不可用時的image
/// </summary>
[
description("按鈕不可用時的image"),
category("appearance"),
editor(typeof(system.web.ui.design.urleditor), typeof(system.drawing.design.uitypeeditor)),
]
public string disabledimage
{
get
{
return statebag.getstring("disabledimage", "");
}
set
{
viewstate["disabledimage"] = value;
}
}
/// <summary>
/// 將此控件呈現給指定的輸出參數。
/// </summary>
/// <param name="output"> 要寫出到的 html 編寫器 </param>
protected override void render(htmltextwriter output)
{
if(appearance == appearanceenum.button)
output.write(getbuttonhtml());
else
output.write(getimagebuttonhtml());
}
/// <summary>
/// 獲取呈現button時的html
/// </summary>
/// <returns></returns>
private string getbuttonhtml()
{
const string buttontag = "<input type=button value='{0}' onclick=/"{1}/" style=/"{2}/"{3} title='{4}'>";
string shtml;
string action;
string style = "width:{0};height:{1};";
if(alertstring != "")
{
action = "javascript:if(window.confirm(/'" + alertstring + "')==true){";
action += page.getpostbackeventreference(this, "click");
action += ";}";
}
else
action = "javascript:" + page.getpostbackeventreference(this, "click");
style = string.format
(
style,
this.width.tostring(),
this.height.tostring()
);
style += this.attributes["style"];
shtml = string.format
(
buttontag,
text,
action,
style,
enabled ? "" : " disabled",
this.tooltip
);
return shtml;
}
/// <summary>
/// 獲取呈現imagebutton時的html
/// </summary>
/// <returns></returns>
private string getimagebuttonhtml()
{
const string linktag = "<a onclick=/"{0}/" title='{1}' style=/"{2}/">{3}</a>";
const string imgtag = "<img src='{0}' border=0>";
string shtml;
string action;
string image;
string style;
if(this.enabled)
{
if(alertstring != "") //僅在用戶確認后調用客戶端的__dostpostback, 引發服務端事件
{
action = "javascript:if(window.confirm(/'" + alertstring + "')==true){";
action += page.getpostbackeventreference(this, "click");
action += ";}";
}
else
action = "javascript:" + page.getpostbackeventreference(this, "click");
if(enabledimage != "")
image = string.format(imgtag, enabledimage);
else
image = text;
}
else
{
action = "javascript:void()";
if(disabledimage != "")
image = string.format(imgtag, disabledimage);
else
image = text;
}
style = "cursor:hand;";
style += this.attributes["style"];
shtml = string.format
(
linktag,
action,
this.tooltip,
style,
image
);
return shtml;
}
protected virtual void onclick()
{
if(click != null)
click(this, eventargs.empty);
}
public void raisepostbackevent(string eventargument)
{
if(eventargument == "click")
onclick();
}
}
}
好了, 到此結束, 將以上代碼編譯為dll, 并加入為控件吧, 試試看, 是不是簡單實用呢?
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